Title

Author

Date of Award

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemistry

Advisor

Hwu, Shiou-Jyh

Committee Member

Kolis, Joseph W

Committee Member

Creager, Stephen

Committee Member

He, Jian

Abstract

The studies demonstrated in this dissertation were primarily focused on the synthesis, structure and property characterizations of iron(II,III) containing framework solids. The scope of this research is threefold: 1) explore new iron(II, III)-containing open framework structures in hopes of creating new materials, useful in the areas of both Li- and Na-ion battery applications; 2) synthesis and characterization of low-dimensional magnetic nanostructures exhibiting novel magnetic properties due to confined magnetic lattices; and 3) conduct structure/property correlation studies to identify the origins of any unusual physical phenomena associated with these new compounds.

In the syntheses of new compounds, molten salt fluxes were utilized due to the refractory nature and low solubility of the covalent transition metal oxides, such as alkali metal chlorides and iodides. Furthermore, the use of eutectic fluxes allowed us to investigate new flux-incorporated compounds via in situ reactions (metathesis reactions). Additionally, oxyanions XO43- (X = P and As) were employed to obtain 3-D Fe-O-X frameworks. Having a poly-anion group in the structure not only increases the Fe3+ /Fe2+ redox couple (due to the inductive effect), regarding potential battery applications but also allows the synthesis of new compounds with magnetic nano-structures embedded in closed-shell, non-magnetic oxyanion matrices. The use of molten salt fluxes allowed for the discovery of several new iron(II,III)-containing phosphates and arsenates for a structure/property correlation study.

Throughout, exploratory syntheses was employed with a typical reaction including various transition metal oxides (Fe2 O3 and/or FeO), main group oxides such as P4 O10 or As2 O 5 , and alkali/alkaline-earth metal oxides. High-temperature solid-state reactions in molten-salt media were utilized in the crystal growth and characterization was performed mainly using single crystal and powder X-ray diffraction. For further property characterizations, techniques and measurements such as electrochemical testing, neutron powder diffraction, magnetic susceptibility measurements, electrical conductivity measurements, electron microscopy, thermal gravimetric analysis, UV-Vis diffuse reflectance and IR were performed.

The new discoveries in this dissertation, mainly, Rb0.41 FePO 4 and A3 Fe6 (XO4 )7 ; A = K, Rb, Cs and X = P and As, have shown fascinating 3-D Fe-O-X frameworks with interesting ion-exchange properties. These new compounds, based on A-Fe-O-X systems where A = larger alkali and alkaline-earth metal cations than Li-ion and these large cations, were used as templates to synthesize new open-frameworks that cannot be initially formed with Li-ions. Sr 1.25 Na1.5 Fe5 O2 (PO4 )5 , another novel open framework structure, was studied as a cathode material for sodium ion batteries due to the interesting channeled structure, see Chapter 5.

Furthermore, these new structures tend to form interesting Fe-O lattices (3-D networks, 2-D sheets, 1-D chains) isolated by diamagnetic poly-anion groups which have been proven to be extremely rich concerning novel magnetic properties. Chapter 6 was aimed on the investigation of the magnetic properties of A 2 Fe2 O(AsO4 )2 ; A = K and Rb with pseudo-one-dimensional Fe-O chains. Moreover, in relation to the investigation of novel magnetic properties, a heterometallic system ( 3d-4f ) was discovered, Rb7 LnFe6 O2 (PO 4 )8 , and the magnetic properties of derivatives where Ln = Sm, Gd and Dy will be discussed. Finally, the structure/property correlations and future development of these newly synthesized compounds should fruitful for the future of battery applications and understanding of novel magnetic phenomena.